Modern sensors vary widely in principle and structure. How to select sensors according to specific measurement purposes, measurement objects and measurement environment is the first problem to be solved when performing a certain amount of measurement.
When the sensor is determined, the matching measurement method and measuring device can be determined. The success or failure of the measurement results depends to a large extent on whether the sensor selection is reasonable.
1. Determine the type of sensor based on the measurement object and the measurement environment
To carry out a specific measurement work, we must first consider what kind of sensor should be used, which needs to be analyzed after analyzing various factors.
Because even if it is measuring the same physical quantity, there are many kinds of sensors available for selection. Which kind of sensor is more suitable, you need to consider the following specific problems according to the characteristics to be measured and the conditions of use of the sensor:
1 size of the range;
2 The position of the measured position on the sensor volume;
3 measurement method is contact or non-contact;
4 signal extraction method, wired or non-contact measurement;
5 The source of the sensor, domestic or imported, the price can withstand, or it is self-developed. After considering the above issues, you can determine which type of sensor to use and then consider the specific performance of the sensor.
2. Sensitivity selection
Generally, in the linear range of the sensor, it is desirable that the sensitivity of the sensor be as high as possible. Because only the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial to signal processing. However, it should be noted that the sensitivity of the sensor is high, and the external noise that is not related to the measurement is easily mixed in, and is amplified by the amplification system, which affects the measurement accuracy. Therefore, the sensor itself should be required to have a high signal-to-noise ratio and minimize interference signals introduced from the outside.
The sensitivity of the sensor is directional. When the measurement is a single vector and its directivity requirements are high, other sensors with small sensitivity should be selected; if the measurement is a multi-dimensional vector, the cross sensitivity of the sensor is required to be as small as possible.
3. Frequency response characteristics
The frequency response characteristics of the sensor determine the frequency range to be measured. The measurement conditions must be kept undistorted within the allowable frequency range. In fact, the response of the sensor always has a certain delay, and the shorter the delay time, the better.
The frequency response of the sensor is high, and the range of the measurable signal frequency is wide, and the inertia of the mechanical system is large due to the structural characteristics, so the frequency of the signal with low frequency can be measured.
In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive errors.
4. Linear range
The linear range of the sensor is the range in which the output is proportional to the input. In theory, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger the range and the guaranteed measurement accuracy. When selecting a sensor, when the type of sensor is determined, it is first necessary to see if its range meets the requirements.
But in reality, any sensor can't guarantee absolute linearity, and its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with less nonlinear error can be approximated as linear, which will bring great convenience to the measurement.
5. Stability
The ability of a sensor to remain unchanged after a period of use is called stability. In addition to the structure of the sensor itself, the factors affecting the long-term stability of the sensor are mainly the environment in which the sensor is used. Therefore, in order to make the sensor have good stability, the sensor must have strong environmental adaptability.
Before selecting a sensor, investigate the environment in which it is used, select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the environmental impact.
The stability of the sensor has quantitative indicators. After the usage period, it should be recalibrated before use to determine whether the performance of the sensor changes. In some cases where the sensor is required for long-term use and cannot be easily replaced or calibrated, the stability of the selected sensor is more stringent and must withstand the test for a long time.
6. Accuracy
Accuracy is an important performance indicator of the sensor, which is an important part of the measurement accuracy of the entire measurement system. The higher the accuracy of the sensor, the more expensive it is. Therefore, the accuracy of the sensor can be as long as it meets the accuracy requirements of the entire measurement system, and it is not necessary to select too high. This makes it possible to select a cheaper and simpler sensor among the many sensors that meet the same measurement purpose.
If the purpose of the measurement is qualitative analysis, the sensor with high repeatability can be selected. It is not suitable to use absolute precision. If it is for quantitative analysis, accurate measurement value must be obtained, and the sensor with the accuracy level can be selected.
For some special applications, if you can't choose the right sensor, you need to design and manufacture the sensor yourself. The performance of the home-made sensor should meet the requirements for use.
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